Add unit tests for functions in wp-includes/category.php.

Props mdbitz. 
Fixes #28119.


git-svn-id: https://develop.svn.wordpress.org/trunk@28566 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/term.php

@@ -325,6 +325,9 @@ class Tests_Term extends WP_UnitTestCase {
 			$this->assertTrue( (bool) wp_delete_post( $post_id, true ) );
 	}
 
+	/**
+	 * @group category.php
+	 */
 	function test_term_is_ancestor_of( ) {
 		$term = rand_str();
 		$term2 = rand_str();